Dimeric and tetrameric cyclopentadienyl group 6b metal alpha-olefin polymerization catalysts and process for polymerizing alpha-olefins

ABSTRACT

Disclosed is a catalyst system for the homopolymerization and copolymerization of alpha-olefins having 2-8 carbon atoms, said catalyst system comprising a dimeric or tetrameric cyclopentadienyl Group 6b metal compound in which the metal has an oxidation state of +2, said Group 6b metal compound being supported on an inorganic support. The catalyst system may also contain a Group 2 or Group 3 metal alkyl compound cocatalyst.

This is a divisional of application Ser. No. 973,139, filed Nov. 6,1992, now U.S. Pat. No. 5,240,895.

FIELD OF THE INVENTION

The present invention relates to catalyst systems for polymerizingalpha-olefins and processes for polymerizing alpha-olefins using suchcatalysts.

BACKGROUND OF THE INVENTION

Chromium based catalysts are used in the commercial polymerization ofsmall alpha-olefins such as ethylene and propylene. One such catalyst isprepared by depositing chromocene (bis(cyclopentadienyl) chromium (II))on an inorganic metal oxide support, as disclosed in British Patent No.1,253,063 to Karapinka. U.S. Pat. No. 4,015,059, issued Mar. 29, 1977 toKarol, describes the use of bis(indenyl)- and bis(flourenyl)-chromium(II) compounds supported on activated inorganic oxide supports ascatalysts for the polymerization of ethylene.

U.S. Pat. No. 4,530,914, issued Jul. 23, 1985 to Ewen et al., disclosesa catalyst system for the polymerization of alpha-olefins whichcomprises two or more metallocenes, each having different propagationand termination rate constants, and aluminoxane. The metallocenes arecyclopentadienyl derivatives of a transition metal of Group 4b, 5b, and6b metals of the Periodic Table. They are described by the formulas (C₅R'_(m))_(p) R"_(s) (C₅ R'_(m))MeQ_(3-p) and R"_(s) (C₅ R'_(m))₂ MeQ'where (C₅ R'_(m)) is a cyclopentadienyl or substituted cyclopentadienyl,each R' is hydrogen or a hydrocarbyl radical, R" is an alkylene radical,a dialkyl germanium or silicon or an alkyl phosphine or amine radicalbridging two (C₅ R'_(m)) rings, Q is a hydrocarbon radical, Me is aGroup 4b, 5b, or 6b metal, s is 0 or 1, p is 0, 1, or 2; when p=0, s=0;m is 4 when s is 1 and m is 5 when s is 0.

U.S. Pat. No. 4,939,217, issued Jul. 3, 1990 to Stricklen, alsodiscloses a process for polymerizing olefins where the polymerization isconducted in the presence of hydrogen, and a catalyst system is usedwhich contains aluminoxane and at least two metallocenes, each havingdifferent olefin polymerization termination rate constants. Themetallocenes disclosed are similar to those described in aforementionedU.S. Pat. No. 4,530,914.

U.S. Pat. No. 4,975,403, issued Dec. 4, 1990 to Ewen, discloses acatalyst system for use in the polymerization of olefins. The catalystsystem includes at least two different chiral, stereo-rigid metallocenecatalysts of the formula R''(C₅ (R')₄)₂ MeQ_(p) (where Me is a Group 4b,5b or 6b metal and (C₅ (R')₄) is a cyclopentadienyl or substitutedcyclopentadienyl ring) and an aluminum compound.

Canadian Patent Application No. 2,000,567, published Apr. 13, 1990,discloses a process for producing polyethylene using a compositecatalyst made up of a solid catalyst component typified by a selectedchromium compound, a modified aluminum compound typified by atrialkylaluminum, and an alkylaluminum alkoxide compound. The chromiumcompound may be chromium oxide, and the modified aluminum compound maybe the reaction product of an organoaluminum compound and water.

European Patent Application Publication No. 416,784 by Dawkins,published Mar. 13, 1991, discloses an olefin polymerization catalystobtainable by depositing on a dry inorganic oxide support a mononuclearchromium complex to produce a catalyst precursor and thereafter bythermally activating the catalyst precursor. The mononuclear chromiumcomplex is representable by the general formula:

    Z--CR--L.sub.x

wherein:

Z is a cyclopentadienyl ligand substituted with 4 or 5 hydrocarbongroups containing 1 to 3 carbon atoms;

x is an integer from 1 to 4, and

L is either a four- or five-substituted cyclopentadienyl ligand, or(CO)₃ R in which R is H, methyl or ethyl.

The catalyst is used to polymerize olefins, particularly ethyleneoptionally with C₃ -C₈ alpha-olefins. The catalyst is said to producepolyolefins having a relatively high molecular weight and a broadmolecular weight distribution.

European patent Application Publication No. 416,785 by Dawkins,published Mar. 13, 1991, also describes an olefin polymerizationcatalyst obtainable by depositing on a dry inorganic oxide at least onemononuclear chromium complex having the general formula:

    Z--Cr--L

wherein:

Z is a cyclopentadienyl ligand substituted with 4 or 5 hydrocarbylgroups containing 1 to 3 carbon atoms; and

L is one or more hydrocarbyl ligands which are sufficiently reactive toenable the complex to react with the inorganic oxide without thermalactivation.

The catalyst can be used without thermal activation for polymerizingolefins, particularly ethylene optionally with C₃ -C₈ alpha-olefins. Thecatalyst is said to produce polyolefins having a broad molecular weightdistribution.

U.S. Pat. No. 4,424,139, issued Jan. 3, 1984 to McDaniel et al.,discloses a catalyst system containing (a) a catalyst Comprising abis-(cyclopentadienyl)-chromium (II) compound and a phosphate-containingsupport and (b) a cocatalyst selected from trihydrocarbyl boranecompounds and aluminum compounds. These catalyst are said to be usefulas olefin polymerization catalysts, and are said to be capable of givingnarrow molecular weight distribution polymer.

A tetrameric chromium (II) compound useful as an alpha-olefinpolymerization catalyst is disclosed in U.S. Pat. No. 4,806,513, issuedFeb. 21, 1989 to McDaniel et al. The compound,octakis-(μ-trimethylsilylmethyl)tetrachromium, is not, however,cyclopentadienyl-containing.

U.S. Pat. No. 4,587,227, issued May 6, 1986 to Smith et al., disclosesoctakis-(μ-trimethylsilylmethyl)tetrachromium on an inorganic oxide as acatalyst to make linear low density polyethylene with specific shortchain branching.

SUMMARY OF THE INVENTION

Recently, new synthetic methods have been developed for preparingdimeric and tetrameric Cr⁺² organometallic compounds. See Heintz, R. A.et al., Angew. Chem., 1992, vol. 104, p. 1100. It has now beendiscovered that when dimeric or tetrameric cyclopentadienyl Cr⁺²compounds are supported on inorganic metal phosphate supports, highproductivity alpha-olefin polymerization catalysts are produced. Inaddition, the use of a cocatalyst improves the productivity of many ofthese compounds. Also, these catalysts produce linear polyethylenes.

In accordance with the present invention, there is provided a catalystsystem for the homopolymerization and copolymerization of alpha-olefinshaving 2-8 carbon atoms, said catalyst system comprising a dimeric ortetrameric cyclopentadienyl Group 6b metal compound in which the metalhas an oxidation state of +2, said Group 6b metal compound beingsupported on an inorganic support.

Also provided in accordance with this invention is a catalyst system forthe homopolymerization and copolymerization of alpha-olefins having 2-8carbon atoms, said catalyst system comprising (a) a dimeric ortetrameric cyclopentadienyl Group 6B metal compound in which the metalhas an oxidation state of +2, said Group 6b metal compound beingsupported on an inorganic support; and, (b) a cocatalyst selected fromGroup 2 or 3 metal alkyl compounds.

Further provided in accordance with the present invention is a processfor the homopolymerization or copolymerization of alpha-olefins having2-8 carbon atoms comprising polymerizing said alpha-olefin, orcopolymerizing two or more alpha-olefins in the presence of a catalystsystem comprising a dimeric or tetrameric cyclopentadienyl Group 6bmetal compound in which the metal has an oxidation state of +2, saidgroup 6b metal compound being supported on an inorganic support.

The present invention also provides a process for the homopolymerizationor copolymerization of alpha-olefins comprising polymerizing saidalpha-olefin, or copolymerizing two or more alpha-olefins in thepresence of a catalyst system comprising (a) a dimeric or tetramericcyclopentadienyl Group 6b metal compound in which the metal has anoxidation state of +2, said group 6b metal compound being supported onan inorganic support, and (b) a Group 2 or 3 metal alkyl compoundcocatalyst.

In the above catalyst systems and processes, chromium is a preferredGroup 6b metal, silica, aluminum phosphate and alumina aluminumphosphate are preferred supports, and aluminoxanes and trialkylaluminumcompounds are preferred Group 2 or 3 metal alkyl compounds.

Among other factors, the present invention is based on the discoverythat the catalyst systems of the present invention have high activity(in terms of amount of polymer produced per amount of chromium per hour)and produce ethylene homopolymers with a high degree of linearity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides catalyst systems for use in thepolymerization (either homopolymerization or copolymerization) of C₂ -C₈alpha-olefins, including ethylene, propylene, 1-butene, 1-hexene,4-methyl-1-pentene, and 1-octene.

It has quite surprisingly been found that, even though the productivityof many cyclopentadienyl Group 6b metal compounds is quite low whenemployed as catalyst in the homogeneous polymerization of alpha-olefins,when these compounds are supported on an inorganic metal oxide orinorganic phosphate solid support, their productivity increasesdramatically, especially when cocatalysts are used. It has now quitesurprisingly been found that dimeric or tetrameric cyclopentadienylGroup 6b metal compounds wherein the metal is in the +2 oxidation statehave activity substantially greater than the mono-nuclear compounds.

While the catalyst systems of the present invention can be used topolymerize a variety of alpha-olefins, they are especially useful in thepolymerization of ethylene. These catalysts produce linear polyethylene,i.e., polyethylene with substantially no side chain branches, in highyield.

The catalyst systems of the present invention comprise at least onedimeric or tetrameric cyclopentadienyl Group 6b metal compound in whichthe Group 6b metal is in an oxidation state of +2, and which iscatalytically active when deposited on an inorganic metal oxide orinorganic metal phosphate support. As used herein, the term"cyclopentadienyl" refers to substituted derivatives of cyclopentadienylin which the cyclopentadienyl ring contains one or more substituentswhich do not interfere with the Group 6b metal compound's ability tofunction as an alpha-olefin polymerization catalyst. Examples ofsubstituted cyclopentadienyl include pentamethylcyclopentadienyl,ethyltetramethylcyclopentadienyl, methylcyclopentadienyl,t-butylcyclopentadienyl, and pentaphenylcyclopentadienyl, as well ascompounds where the substituent forms a multi-cyclic ring with thecyclopentadienyl ring. Examples of these multi-cyclic rings includeindenyl and fluorenyl rings. For the sake of simplicity, theabbreviation Cp.sup.. will be used herein to refer topentamethylcyclopentadienyl, and the abbreviation Cp' will be usedherein to refer to ethyltetramethylcyclopentadienyl. Cp^(*) and Cp' arepreferred cyclopentadienyl groups as they stabilize the organometalliccompound of this invention.

The Group 6b metal compounds useful in the present invention includecompounds wherein the metal is chromium, molybdenum or tungsten.Compounds in which the metal is chromium are preferred. The Group 6bmetal atom in the compound has an oxidation state of +2.

The Group 6b metal dimers have, in addition to one cyclopentadienylgroup, at least one hydrocarbyl group bonded to each metal atom. As usedherein, the term "hydrocarbyl" refers to alkyl, alkenyl, aryl, aralkyland alkaryl radicals and the like. Exemplary hydrocarbyl radicalsinclude, but are not limited to, methyl, ethyl, propyl, butyl, amyl,isoamyl, hexyl, neopentyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl,phenyl, benzyl and other similar groups. Additionally, organosilylgroups which are bonded to the chromium atom(s) through a carbon atomcan be used. Trimethylsilyl methyl, i.e., (CH₃)₃ SiCH₂ --, and the likeare examples of such organosilyl groups. If more than one hydrocarbylgroup is bonded to the metal atom, they can be independent or linked,i.e., they can form a 3-, 4-, 5-, 6-, or 7-membered metallocycle. TheGroup 6b metal tetramers have, in addition to one cyclopentadienyl groupbonded to each metal atom, an hydride group also attached to each metalatom.

One object of this invention is to provide a catalyst and a process forproducing linear, high density polyethylene with high molecular weightand narrow molecular weight distribution, using a dimeric or tetramericcyclopentadienyl Cr⁺² catalyst.

The strong chromium-chromium multiple bond present in [Cp^(*) Cr(CH₃)]₂makes it virtually unreactive towards ethylene and dative ligands suchas tetrahydrofuran and pyridine (see the aforementioned Heintz et al.article). Quite surprisingly, it has been found that depositing [Cp^(*)Cr(CH₃)]₂ on a solid support generates a highly active ethylenepolymerization catalyst. This dramatic difference in polymerizationreactivity between supported and unsupported organometallic complexes isnot readily or reliably predicted.

Examples of the Group 6b metal compounds useful in this inventioninclude, but are not limited to, compounds having the following generalformula:

    [(C.sub.5 (R').sub.5)MX].sub.a                             (I)

wherein M is a Group 6b metal such as chromium, molybdenum and tungsten;

(C₅ (R')₅) is a substituted cyclopentadienyl ring,

R' is at each independent occurrence hydrogen, a hydrocarbyl radicalhaving 1-20 carbon atoms, or adjacent R' groups may together form one ormore hydrocarbyl rings, with the proviso that at least one R' is alkyl;

a=2 or 4;

X is at each independent occurrence a hydrocarbyl radical having 1-20carbon atoms (for example, a monovalent saturated aliphatic or alicyclicradical or a monovalent aryl or alkyaryl radical, or combinationsthereof), or an organosilyl group, such as trimethylsilylmethyl, whena=2, or hydrogen when a=4.

Examples of compounds having formula (I) above include, but are notlimited to, [Cp^(*) Cr(CH₃)]₂, [Cp^(*) Cr(Bzyl)]₂, [Cp^(*) Cr(Ph)]2,[Cp^(*) Cr(TMSM)]₂, where Bzyl is benzyl, Ph is phenyl, and TMSM istrimethylsilylmethyl.

In part, the choice of Group 6b metal compound is based on the thermalstability of the compound and its ease of preparation. Of the Group 6bmetal compounds useful in this invention, the organochromium compoundsare preferred.

In the catalyst systems of the present invention, the Group 6b metalcompound is deposited on an inorganic support. Suitable inorganic metaloxide supports include silica, alumina, silica-alumina mixtures, thoria,zirconia, magnesium oxide and similar oxides. Suitable inorganic metalphosphates include aluminum phosphate, zirconium phosphate,magnesium-containing alumina phosphate and alumina aluminum phosphate.Silicas, aluminum phosphates and alumina aluminum phosphates arepreferred. Suitable silica supports include Davison 952, Davison 955,Crosfield Ep-10 and Crosfield EP17MS. Further examples of usefulsupports are the following: alumina aluminum phosphates with aluminum tophosphorus ratios of about 5:1 to 1:1 as disclosed in U.S. Pat. Nos.4,080,311 and 4,219,444; magnesia-alumina-aluminum phosphates asdescribed in U.S. Pat. No. 4,210,560; zinc oxide-cadmiumoxide-alumina-aluminum phosphates such as those disclosed in U.S. Pat.No. 4,367,067; and the calcium, barium, and/or strontiumoxide-alumina-aluminum phosphates described in U.S. Pat. Nos. 4,382,877and 4,382,878. The acidity of these supports can be adjusted byjudicious inclusion of basic metals such as alkali and alkaline earthmetals (Ca, Be, Mg, K, Li) to counteract excessive acidity. Other usefulsupports include magnesium halides, particularly magnesium chloride,such as those described in "Transition Metals and Organometallics asCatalysts for Olefin Polymerization" (1988, Springer-Verlag) edited byW. Kaminsky and H. Sinn and "Transition Metal CatalyzedPolymerizations-Ziegler-Natta and Metathesis Polymerizations" (1988,Cambridge University Press) edited by R. Quirk.

The supports useful in this invention should have a high surface area.In general, these supports should have the characteristics listed in thefollowing table:

    ______________________________________                                        Property     Broad Range  Preferred Range                                     ______________________________________                                        Surface area 25-600 m.sup.2 /g                                                                          100-370 m.sup.2 /g                                  Pore volume  0.25-4 cm.sup.3 /g                                                                         0.7-3 cm.sup.3 /g                                   Mean particle                                                                              30-200 microns                                                                             60-140 microns                                      diameter                                                                      ______________________________________                                    

Preferably, the pore size distribution is broad, with a significantpercentage of the pores in the macropore range (>500 Angstroms)Preferably, at least 50% of the pores are macropores. It is alsodesirable that the support be substantially anhydrous before the Group6b metal compound is deposited on it. Thus, it is desirable to calcinethe support prior to deposition of the Group 6b metal compound.

The supported catalysts of this invention are readily prepared bytechniques well known in the art. For example, a solution of the Group6b metal compound in aliphatic, aromatic or cycloaliphatic hydrocarbons,or ethers such as diethyl ether or tetrahydrofuran can be stirred withthe support until the Group 6b metal compound is adsorbed on or reactedwith the support. The amount of Group 6b metal compound relative to theamount of support will vary considerably depending upon such factors asthe particle size of the support, its pore size and surface area, thesolubility of the Group 6b metal compound in the solvent employed, andthe amount of Group 6b metal compound which is to be deposited on thesupport. However, in general the amount of Group 6b metal compound usedis adjusted so that the final metal content (calculated as the element),relative to the support, is in the range of from about 0.01 to about 10weight percent. In most cases, the most desirable level is in the rangeof about 0.1 to about 5 weight percent.

Activities for the catalyst systems of the present invention are greaterthan 3,000 grams of polymer per gram of chromium metal per hour ("g/gCr/hr"), preferably greater than 30,000 g/g Cr/hr, and more preferablygreater than 200,000 g/g Cr/hr.

It has been found that the activity of many of the supported Group 6bmetal dimers and tetramers of this invention is significantly increasedwhen they are employed in conjunction with a co-catalyst. Theco-catalysts useful in the practice of the present invention are Group 2and Group 3 metal alkyls. As used herein, the term "Group 2 and Group 3metal alkyls" refers to compounds containing a metal from Group 2 orGroup 3 of the Periodic Table (such as Mg, Zn, B, or Al) to which isbonded at least one alkyl group, preferably a C₁ to C₈ alkyl group.Suitable Group 2 and Group 3 metal alkyls include dialkyl magnesium,dialkyl zinc, trialkylboranes, and aluminum alkyls. Suitable aluminumalkyls include trialkylaluminums (such as trimethylaluminum,triethylaluminum, triisobutylaluminum and trioctylaluminum).Trialkylaluminums with alkyl groups of four carbons or greater arepreferred. Other aluminum alkyls useful in the practice of the presentinvention include alkylaluminum alkoxides (such as diethylaluminumethoxide and ethylaluminum diethoxide), and alkylaluminum halides (suchas diethylaluminum chloride, diethylaluminum bromide, diethylaluminumiodide, diethylaluminum fluoride, ethyl aluminum dichloride, ethylaluminum dibromide, ethyl aluminum diiodide, ethyl aluminum difluoride,and ethyl aluminum sesquichloride).

Other suitable aluminum alkyls are aluminoxanes, including thoserepresented by the general formula (R-Al-O)_(n) for the cyclic form andR(R-Al-O)_(n) -AlR₂ for the linear form. In these formulas, R is, ateach independent occurrence, an alkyl group (such as methyl, butyl,isobutyl and the like) preferably with more than two carbon atoms, morepreferably with 3-5 carbon atoms, and n is an integer, preferably from 1to about 20. Most preferably, R is an isobutyl group. Mixtures of linearand cyclic aluminoxanes may also be used. Examples of aluminoxanesuseful in this invention include, but are not limited to, ethylaluminoxane, isobutyl aluminoxane, and methyl aluminoxane. Aluminoxanes(also known as "alumoxanes") suitable for use in this invention aredescribed in Pasynkiewicz, "Alumoxanes: Synthesis, Structure, Complexesand Reactions," Polyhedron 9, p. 429 (1990), which is incorporated byreference herein in its entirety.

The preferred Group 2 and Group 3 metal alkyls are the aluminoxanes andthe trialkylaluminums.

When used, the Group 2 and Group 3 metal alkyls are used in a Group 2 or3 metal alkyl to Group 6b metal compound mole ratio of from about 1:1 toabout 1000:1. The preferred mole ratio is from about 10:1 to about200:1.

The catalyst systems of the present invention may be used in eitherslurry or gas phase polymerization processes. After the catalysts havebeen formed, the polymerization reaction is conducted by contacting themonomer charge with a catalytic amount of the catalyst at a temperatureand at a pressure sufficient to initiate the polymerization reaction. Ifdesired, an organic solvent may be used as a diluent and to facilitatematerials handling. The polymerization reaction is carried out attemperatures of from about 30° C. or less up to about 200° C. or more,depending to a great extent on the operating pressure, the pressure ofthe entire monomer charge, the particular catalyst being used, and itsconcentration. Preferably, the temperature is from about 30° C. to about125° C. The pressure can be any pressure sufficient to initiate thepolymerization of the monomer charge, and can be from atmospheric up toabout 1000 psig. As a general rule, a pressure of about 20 to about 800psig is preferred.

When the catalyst is used in a slurry-type process, an inert solventmedium is used. The solvent should be one which is inert to all othercomponents and products of the reaction system, and be stable at thereaction conditions being used. It is not necessary, however, that theinert organic solvent medium also serve as a solvent for the polymerproduced. The inert organic solvents which may be used include saturatedaliphatic hydrocarbons (such as hexane, heptane, pentane, isopentane,isooctane, purified kerosene and the like), saturated cycloaliphatichydrocarbons (such as cyclohexane, cyclopentane, dimethylcyclopentane,methylcyclopentane and the like), aromatic hydrocarbons (such asbenzene, toluene, xylene and the like), and chlorinated hydrocarbons(such as chlorobenzene, tetrachloroethylene, o-dichlorobenzene and thelike). Particularly preferred solvents are cyclohexane, pentane,isopentane, hexane and heptane.

When the catalyst is used in a gas phase process, it is suspended in afluidized bed with, e.g., ethylene. Temperature, pressure and ethyleneflow rates are adjusted so that to maintain acceptable fluidization ofthe catalyst particles and resultant polymer particles. Furtherdescriptions of such a fluidized bed may be found in British Patent No.1,253,063, to Karapinka, which is incorporated by reference herein.

The term molecular weight distribution ("MWD"), as used herein, is theweight average molecular weight ("M_(w) ") divided by the number averagemolecular weight ("M_(n) "), i.e., M_(w) /M_(n). In general, thepolymers which have high MWD's have improved ease of processing, bettermelt behavior, and other desirable properties such as impact resistanceand environmental stress crack resistance. Large blow molded productsare superior when made with high MWD polymers. Additionally, film ismore puncture resistant when made from polymer with a high MWD. Thepolymers made in accordance with this invention using alumina aluminumphosphate supported catalysts possess high molecular weight and a morenarrow MWD, making them useful in such applications as injectionmolding.

It has quite surprisingly been found that when the catalyst systems ofthis invention are used to produce ethylene homopolymers, the resultingpolyethylenes are highly linear, whereas ethylene homopolymers preparedusing similar catalyst systems contain significant amounts of side chainbranching. This is demonstrated by ¹³ C NMR analysis where, for example,polyethylene prepared in accordance with the present invention using[Cp.sup.. CrCH₃ ]₂ supported on Al₂ O₃.2AlPO₄ with IBAO cocatalyst has 0side chain branches ("SCB") per 1000 carbon atoms in the polyethylene.In contrast, polyethylenes made using bis-(cyclopentadienyl)chromium(II) (i.e , chromocene) supported on AlPO₄ are reported to contain 0.6to 0.7 mole percent of side chain branches (see U.S. Pat. No.4,424,139). We have also observed side chain branching (1.5 SCB/1000carbon atoms) for catalysts containing chromocene supported ondehydrated silica (see Run 6 in Comparative Example A below).

Further, it has been found that, in contrast to supported Cr₄ (TMSM)₈catalysts which produce polymer with extremely broad molecular weightdistributions (MWD=140, see Run 7 in Comparative Example A below), thecatalysts of the present invention yield polymer with extremely narrowMWD (see Runs 1-5 in Example 4 below). This surprising resultunderscores the unpredictable nature of supported organochromiumcatalysts and their polymerization products.

The following examples are intended to further illustrate the presentinvention, and are not intended to limit its scope.

EXAMPLE 1 PREPARATION OF [Cp.sup.. CrCH₃ ]₂

[Cp^(*) CrCH₃ ]₂ was prepared by a procedure similar to that disclosedin the aforementioned Heintz et al. article.

To a stirring slurry of 216 mg CrCl₂ (anhydrous) in 50 ml THF was added250 mg of LiCp^(*). The resulting dark blue solution was stirredovernight and the next day the THF was stripped off using arotoevaporator. The resulting solid was then dissolved in pentane andfiltered. The solution was concentrated and the solid recrystallized at-30° C. The yield was 65%.

The isolated [Cp.sup.. Cr(u-Cl]₂ was then dissolved in diethyl ether andone equivalent of methyllithium was added via syringe. The resultingsolution was filtered and the ether removed by rotoevaporation. Theresulting solid was recrystallized from pentane at -30° C. to give theproduct.

The reaction can also be done in a single reaction vessel withoutisolating [Cp.sup.. Cr(u-Cl]₂.

EXAMPLE 2 PREPARATION OF [Cp'CrH]₄

[Cp'CrH]₂ is prepared in a manner similar to that disclosed in theaforementioned Heintz et al. article.

EXAMPLE 3 PREPARATION OF SUPPORTED CATALYSTS

Silica supports were purchased from W. R. Grace & Co., and includedDavison 952 and Davison 955 silicas. These silicas have the followingproperties:

    ______________________________________                                        Property      Davison 952  Davison 955                                        ______________________________________                                        Surface area  340 m.sup.2 /g                                                                             300 m.sup.2 /g                                     Pore volume   1.68 cm.sup.3 /g                                                                           1.60 cm.sup.3 /g                                   Mean particle 110 microns  40 microns                                         diameter                                                                      ______________________________________                                    

The alumina aluminum phosphate supports used in the following exampleswere prepared by the procedure of Example 1 in U.S. Pat. No. 4,080,311,issued Mar. 21, 1978 to Kehl, which patent is incorporated by referenceherein. The product had an Al₂ O₃ to AlPO₄ ratio of 1:2.

All catalysts were prepared in a similar manner. Details for [Cp^(*)CrCH₃ ]₂ are as follows: [Cp^(*) CrCH₃ ]₂ (0.040 g, 9.89 ×10⁻⁵ moles)was dissolved in 10 ml of pentane and treated all at once with 1.00 gAl₂ O₃.2AlPO₄. The solution was stirred for 15 minutes resulting in ablue-purple solid and clear supernatant. The solid was collected, washedwith 2×10 ml of pentane and dried under vacuum to a free-flowing powder.

In addition, Cr₄ (TMSM)₈ was prepared as described in aforementionedU.S. Pat. No. 4,806,513. Cr₄ (TMSM)₈ and chromocene were each in turnsupported in a manner identical to that described above. The resultingcatalysts were dark brown in color and contained about 1.0 wt % Cr.

EXAMPLE 4 ETHYLENE POLYMERIZATION USING SUPPORTED CATALYST

Polymerization runs were conducted in 1 or 2 liter autoclave reactorsunder particle form (slurry) conditions using between 300 and 500 mlheptane as diluent, and a weighed amount of catalyst (typically 0.050 to0.250 g). Run times of 0.5 to 1.0 hour were normally employed. Forexample, in a typical run, 0.100 g of the catalyst prepared in Example 1([Cp^(*) CrCH₃ ]₂ adsorbed on Al₂ O₃.2AlPO₄) was charged to a one-literautoclave along with 300 ml of heptane. Polyisobutylaluminoxane (0.5 mlof a 1.0M heptane solution, prepared by slow hydrolysis oftriisobutylaluminum with 1.0 equivalents of H₂ O as in Example 3 of U.S.Pat. No. 4,665,208, issued May 12, 1987 to Welborn et al., which patentis incorporated by reference herein) was added to the stirred reactor ascocatalyst. The reactor temperature and pressure were adjusted to 85° C.and 550 psi (with ethylene), respectively. The ethylene was supplied ondemand from a pressurized reservoir. After 0.5 hour, the reaction wasstopped by rapidly cooling the reactor and venting the pressure. Thepolymer produced was washed with isopropanol and acetone, and driedunder vacuum to yield 82.9 g of white, granular solid. The results ofthese polymerizations are indicated in Tables I-IV.

                  TABLE I                                                         ______________________________________                                        POLYMERIZATION DATA FOR [Cp*CrCH.sub.3 ].sub.2                                     Sup-    u mol   Co-          C.sub.2 H.sub.4                                                                    Temp, Acti-                            Run  port    Cr      catalyst                                                                             Al:Cr.sup.a                                                                         psig °C.                                                                          vity.sup.b                       ______________________________________                                        1    ALPO.sup.c                                                                            39.6    None   0     550  85     94,000                          2    ALPO    39.6    None   0     550  85    114,000                          3    ALPO    39.6    None   0     550  80     39,000                          4    ALPO     5.9    IBAO.sup.d                                                                           17    550  80    638,000                          ______________________________________                                         .sup.a Mole ratio                                                             .sup.b Activity is expressed in g. polymer/g. Cr/hr.                          .sup.c ALPO = Al.sub.2 O.sub.3.2AlPO.sub.4                                    .sup.d IBAO = Isobutylaluminoxane                                        

                  TABLE II                                                        ______________________________________                                        ANALYTICAL DATA FOR POLYETHYLENES                                             PREPARED WITH [Cp*CrCH.sub.3 ].sub.2                                                          Density     MW.sup.e ×                                  Run     T.sub.m, °C.                                                                   g/cc        10.sup.-3                                                                            MWD                                        ______________________________________                                        1       --      0.9297      862    3.73                                       2       137.1   0.9331      818    2.50                                       3       138.4   0.9322      734    2.35                                       4       137.8   0.9301      791    2.23                                       ______________________________________                                         .sup.e Determined by GPC.                                                

                  TABLE III                                                       ______________________________________                                        POLYMERIZATION DATA FOR [Cp'CrH].sub.4                                             Sup-    u mol   Co-          C.sub.2 H.sub.4                                                                    Temp, Acti-                            Run  port    Cr      catalyst                                                                             Al:Cr psig °C.                                                                          vity                             ______________________________________                                        5    ALPO    15.9    IBAO   19    550  80    516,000                          ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        ANALYTICAL DATA FOR POLYETHYLENES                                             PREPARED WITH [Cp'CrH].sub.4                                                                  Density     MW ×                                        Run     T.sub.m, °C.                                                                   g/cc        10.sup.-3                                                                            MWD                                        ______________________________________                                        5       135.5   0.9310      893    4.54                                       ______________________________________                                    

COMPARATIVE EXAMPLE A

Polymerization runs were conducted in a manner similar to that describedin Example 4 using as catalyst, each in turn, chromocene (Cp₂ Cr)supported on dehydrated silica and Cr₄ (TMSM)₈ supported on Al₂O₃.2AlPO₄.

The results are indicated in Tables V and VI below.

                                      TABLE V                                     __________________________________________________________________________    POLYMERIZATION DATA FOR Cp.sub.2 Cr and Cr.sub.4 (TMSM).sub.8                                   u mol                                                                             Co-      C.sub.2 H.sub.4                                                                  Temp,                                       Run                                                                              Catalyst                                                                             Support Cr  catalyst                                                                           Al:Cr                                                                             psig                                                                             °C.                                                                        Activity                                __________________________________________________________________________    6  Cp.sub.2 Cr                                                                          SiO.sub.2.sup.e                                                                       10.2                                                                              IBAO 29.5                                                                              200                                                                              80  170,000                                 7  Cr.sub.4 (TMSM).sub.8                                                                Al.sub.2 O.sub.3.2AlPO.sub.4.sup.f                                                    30.3                                                                              IBAO 10.2                                                                              550                                                                              80  145,000                                 __________________________________________________________________________     .sup.e Crosfield EP10, dehydrated at 600° C. for 24 hours.             .sup.f Dehydrated at 400° C. for 24 hours.                        

                  TABLE VI                                                        ______________________________________                                        ANALYTICAL DATA FOR POLYETHYLENES PRE-                                        PARED WITH Cp.sub.2 Cr AND Cr.sub.4 (TMSM).sub.8                              Run  Catalyst   T.sub.m, °C.                                                                   Density                                                                              SCB.sup.g                                                                           MW.sup.h                                                                            MWD                                ______________________________________                                        6    Cp.sub.2 Cr                                                                              137.1   0.9316 1.5   907,000                                                                             3.01                               7    Cr.sub.4 (TMSM).sub.8                                                                    131.8   0.9572 --    384,000                                                                             144                                ______________________________________                                         .sup.g SCB = side chain branches per 1000 carbon atoms.                       .sup.h Determined by GPC.                                                

EXAMPLE 5 GAS PHASE POLYMERIZATION

The procedure of Example 4 is repeated in a 2 liter, stirred autoclaveusing the supported catalysts of this invention, except that heptane isnot added to the autoclave. The reactor temperature and pressure areadjusted to 85° C. and 550 psi (with ethylene), respectively. A white,granular polymer is produced.

What is claimed is:
 1. A process for the polymerization of olefins,which comprises homopolymerizing or copolymeizing olefins selected fromthe group consisting of ethylene and alpha-olefins of 3-8 carbon atomsin the presence of a catalyst system comprising a dimeric or tetramericcyclopentadienyl chromium compound in which chromium metal has anoxidation state of +2, said chromium compound being supported on aninorganic support.
 2. The process of claim 1 wherein the chromiumcompound has the formula:

    [(C.sub.5 (R').sub.5)CrX].sub.a

wherein (C₅ (R')₅) is a substituted cyclopentadienyl ring; R' is at eachindependent occurrence hydrogen, a hydrocarbyl radical having 1-20carbon atoms, or adjacent R' groups may together form one or morehydrocarbyl rings with the proviso that at least one R' is alkyl; a=2 or4; X is at each independent occurrence a hydrocarbyl radical having 1-20carbon atoms or an organosilyl group when a=2, or hydrogen when a=4. 3.The process of claim 2 wherein (C₅ (R')₅) ispentamethylcyclopentadienyl.
 4. The process of claim 2 wherein (C₅(R')₅) is ethyltetramethylcyclopentadienyl.
 5. The process of claim 2wherein X is selected from the group consisting of methyl, benzyl andtrimethylsilylmethyl.
 6. The process of claim 2 wherein the chromiumcompound is selected from

    [Cp.sup.* CrCH.sub.3 ].sub.2

    [Cp'CrH].sub.4

where Cp^(*) is pentamethylcyclopentadienyl and Cp' isethyltetramethylcyclopentadienyl.
 7. The process of claim 1 wherein thesupport is an inorganic metal oxide or inorganic metal phosphate.
 8. Theprocess of claim 7 wherein the support is selected from the groupconsisting of alumina, silica, silica-alumina, aluminum phosphate,zirconium phosphate, and alumina aluminum phosphate.
 9. The process ofclaim 8 wherein the support is selected from silica, aluminum phosphateand alumina aluminum phosphate.
 10. The process of claim 9 wherein thesupport is alumina aluminum phosphate.
 11. The process of claim 6wherein the support is selected from the group consisting of alumina,silica, silica-alumina, aluminum phosphate, zirconium phosphate, andalumina aluminum phosphate.
 12. The process of claim 11 wherein thesupport is selected from silica, aluminum phosphate and alumina aluminumphosphate.
 13. The process of claim 12 wherein the support is aluminaaluminum phosphate.
 14. A process according to claim 1 wherein thechromium of said chromium compound is present in an amount within therange of 0.1 to 10 weight percent based on the weight of said inorganicsupport.
 15. A process for the homopolymerization of alpha-olefin having2-8 carbon atoms or copolymerization of alpha-olefins having 2-8 carbonatoms, comprising homopolymerizing said alpha-olefin, or copolymerizingtwo or more said alpha-olefins, in the presence of a catalyst systemcomprising:(a) a dimeric or tetrameric cyclopentadienyl chromiumcompound in which chromium metal has an oxidation state of +2, saidchromium compound being supported on an inorganic support; and (b) acocatalyst selected from Group 2 or 3 metal alkyl compounds.
 16. Theprocess of claim 15 wherein the chromium compound has the formula:

    [(C.sub.5 (R').sub.5)CrX].sub.a

wherein (C₅ (R')₅) is a substituted cyclopentadienyl ring; R' is at eachindependent occurrence hydrogen, a hydrocarbyl radical having 1-20carbon atoms, or adjacent R' groups may together form one or morehydrocarbyl rings with the proviso that at least one R' is alkyl; a=2 or4; X is at each independent occurrence a hydrocarbyl radical having 1-20carbon atoms or an organosilyl group when a=2, or hydrogen when a=4. 17.The process of claim 16 wherein (C₅ (R')₅) ispentamethylcyclopentadienyl.
 18. The process of claim 16 wherein (C₅(R')₅) is ethyltetramethyl cyclopentadienyl.
 19. The process of claim 16wherein said hydrocarbyl radical is selected from the group consistingof methyl, benzyl and trimethylsilylmethyl.
 20. The process of claim 16wherein the chromium compound is selected from

    [Cp.sup.* CrCH.sub.3 ].sub.2

    [Cp'CrH].sub.4

where Cp^(*) is pentamethylcyclopentadienyl and Cp' isethyltetramethylcyclopentadienyl.
 21. The process of claim 15 whereinthe support is an inorganic metal oxide or inorganic metal phosphate.22. The process of claim 21 wherein the support is selected from thegroup consisting of alumina, silica, silica-alumina, aluminum phosphate,zirconium phosphate, and alumina aluminum phosphate.
 23. The process ofclaim 22 wherein the support is selected from silica, aluminum phosphateand alumina aluminum phosphate.
 24. The process of claim 23 wherein thesupport is alumina aluminum phosphate.
 25. The process of claim 20wherein the support is selected from the group consisting of alumina,silica, silica-alumina, aluminum phosphate, zirconium phosphate, andalumina aluminum phosphate.
 26. The process of claim 25 wherein thesupport is selected from silica, aluminum phosphate and alumina aluminumphosphate.
 27. The process of claim 26 wherein the support is aluminaaluminum phosphate.
 28. The process of claim 15 wherein the chromium ofsaid chromium compound is present in an amount within the range of 0.1to 10 weight percent based on the weight of said inorganic support. 29.The process of claim 15 wherein the Group 2 or Group 3 metal alkylcompound is an alkylaluminum compound.
 30. The process of claim 29wherein the alkylaluminum compound is selected from the group consistingof trialkylaluminum compounds, alkylaluminum alkoxides, alkylaluminumhalides and aluminoxanes.
 31. The process of claim 26 wherein thealkylaluminum compound is an aluminoxane or trialkylaluminum compound.32. A process according to claim 31 wherein the alkylaluminum compoundis isobutylaluminoxane.